[android] build and run LIT-based tests on x64

[weliveindetail]

The Swift SDK contains components that use the LLVM Integrated Tester, e.g. swift-corelibs-xctest

Tests in swift-corelibs-xctest are implemented in Swift, so we have to make the Swift Runtime available on the emulator. The lit.cfg in swift-corelibs-xctest seems to allow us to inject SWIFT_EXEC, SWIFT_FLAGS and FOUNDATION_BUILT_PRODUCTS_DIR as environment variables. There are special cases for Windows already, we might have to add some upstream for Android.

LIT tests have end-to-end character: Test conditions and behavior is described in text files that are parsed from Python. RUN lines invoke executables and pass arguments, so the command-line is the interface to the code under test here.

[weliveindetail]

There might be infrastructure in LIT that allows to offload test execution. This bot cross-compiles upstream LLVM for Android and (apparently) runs tests on attached devices: https://lab.llvm.org/buildbot/#/builders/186

[compnerd]

Yes, there is existing tooling that needs to be understood that allows sharding and remote execution under an emulator that we should try to reuse if possible.

[weliveindetail]

For the moment I found a few related mechanisms, but none of them exactly matches what we are looking for:

• COMPILER_RT_EMULATOR is a feature of compiler-rt that seems very close, but I'd have to implement it for the projects we want to support.
• TEST_SUITE_RUN_UNDER is a feature of LNT, the nightly test suite. We don't use that.
• There are scattered bits of Apple-specific code that add support for iOS simulators.

[weliveindetail]

The Swift test suite itself ships a number of adb utility scripts that are wired up in the main LIT file via the target_run configuration (which is used for Apple simulators as well):
https://github.com/swiftlang/swift/blob/eb6339dd3ec241cb56965a18a7c171ddd6bd2809/test/lit.cfg#L1947

It looks like we can us this approach for all Swift tests (except swift_interpreter, which is discarded explicitly). In a first step we could try and use it for the existing compiler-rt components. If that works, we may find a way to extend it to the out-of-tree Swift Runtime libraries.